THREE-DIMENSIONAL RAPID PROTOTYPING

Abstract: A method of automated layer-wise fabrication of a three-dimensional part from a computer model through controlled deposition and extraction of materials. The method integrates the precision control of established subtractive processes with additive processes optimised to produce desired material properties in order to produce a superior rapid prototyping system that does not suffer from the short-comings of prior art systems.

Description: THREE-DIMENSIONAL RAPID PROTOTYPING The present invention relates to methods of prototype constiuction and/or small quantity manufacture by controlled layerwise deposition and extraction. BACKGROUND OF THE INVENTION There is considerable interest within industry in manufacturing prototypes or small production batches in a rapid and cost effective manner. Conventional part production methods are neither time nor cost effective when only a small number of units are needed because they require expensive part-specific tooling, setting up machining protocols, and generating and programming three- dimensional (3-D) tool paths which require much time and professional expertise. The cost and time to set up and run machine-specific tooling, along with the initial capital costs for tooling, make conventional prototyping small production run processes both time and cost intensive. Furthermore, conventional prototyping methods are limited in practice to simple part geometries. Complex parts involving inner features and corcs/cavitics aie difficult to produce using conventional techniques and often require precision casting methods which arc highly expensive, lime consuming, and require a hioad range ol expei lise. Rapid Prototyping Systems (RPS) in the prior art, lo a large degree, attempts to address the needs and problems mentioned above Λ single automated system can be used to produce prototype parts and small production runs direct ly from engineering designs. Such a system is limited only by the size of the part and not by the intricacy of the part geometry. Thus, such a machine is not so part-specific as conventional tooling, and a capital investment in such a machine is all thai is needed to produce virtually any part within the size constraints of the system. Automated prototyping machines, furthermore, require a minimum of human expertise lor successful operation and a relatively negligible amount of set up time for a particular part. Parts of complex geometries can be realized in relatively short amounts of lime with significant benefit to industry especially where designs are changed frequently and prototypes or mock-ups are needed for design evaluation. All such RPS make use of a common approach involving the stratification of the prototype. Software "slices" the prototype part geometry into a sequence of cross-sectional contours(strala) used to drive a materials processing system which recreates each contour out of prespecified materials. The prototype part is built up by adhering successive part cross-sections together until the part is complete Currently, there are several realizations of RPS, each employing a particular technology with its own strengths and weaknesses: Slercolithography, referenced in US patent 4,575,330 by Charles W. Mull; * Computer Aided Manufacturing Process and System (CAMPS), as described in US patent 4,665,492 by William E. Masters; * Laminations Method, described in US patent 4,752,352 by Michael Feygin; Selective Laser Sintering (SLS), described in US patent 4,863,538 by Carl R. Deckard; • |: Mask and Deposit (MD '|; ) System, described in US patent 5,126,529 by Lee F. Weiss. * Three Dimensional Printing, discussed in the Publication " Three Dimensional Printing: norm, Materials, and Performance ", by Michael .1. Cima and πmanuel M. Sachs, Solid Free form Fabrication Symposium, University of Texas at Austin, Austin TX, August 1991. Stcicolithography produces part layers by scanning a laser across the surface of a photopolymei" liquid bath and curing the pholopolyincr along the part contours. The precision is only limited by the boundary of photopolymerizalion initially, but as the parts continue curing in the post build stage, wai page becomes a limiting factor. The material properties of the parts arc also limited by the material properties of photopolyiners. Selective laser Sintering (SLS) produces part layers by scanning powder with a high powered laser to induce sintering local to the laser path. While this process creates complicated geometries, the sintered material densities arc low. Consequently, the mechanical properties of SLS parts arc relatively unsuitable for functional prototypes. Increasing the density of SLS parts would require a higher degree of .sintering/melting of the part powder, thereby compromising the geometric control provided by SLS. Rapid prototyping by Precision Metal Spraying (Mask and Deposition the other hand, employs precision cut masks for each part layer and thus has the advantage of geometric control limited by the mask precision and/or the aspect ratio (mask feature width -to-laycr depth), notwithstanding any problems associated with mask/part material selection such as binding, warping, and mask melting. The inlra/intci layer bonding in sprayed parts, however, is often primarily mechanical because the material pai tides are cooled before they hit the surface layer. Obtaining stress-free layers with desirable material properties involves significant tradeoffs with geometric control of the part. Similarly, parts made by Ballistic Particle Manufacturing or InkJet Printing (CAMPS) must also trade off part quality with geometric control. The building of prototypes from welded or adhered precul laminations as in the Laminations Method, moreover, suffers from a tradeoff between inter -lamination bonding and gcoineli ic control, as well as from sevei al precision handling problems associated with complicated pail cross sections. Lastly, 3-D printing systems deposit tiny binder material droplets onto a layer of powder, essentially precision printing each successive part layer. These systems, however, have the disadvantage of porosity (low density) and poor bonding in green parts (prior to oven baking) due lo the lluid mechanics and physics til the printing and binding processes. Once the parts arc oven heated to bake out the binder material, warpage and distortion related to shrinkage limit the attainable precision of the final parts. All of the present rapid prototyping methods, therefore, unfortunately are subject lo contain inherent difficulties and limitations in aspects of their prototype creation. In summary, the key disadvantages associated with one or more of the current systems arc: ( I ) poor material properties and/or distribution of material properties; (2) poor geometric control and/or difficulty with complex geometry; and (3) trade off between geometric part control and intcrlaycr bond strength and/or part properties, such as density or inicrostructure. While each of the above prior processes is different, they all share a key clement: each process is additive That is, they all produce a 3-D part by incrementally adding material to built it up. Furthermore, the additive technologies which distinguish these processes all involve a tradeoff between maintaining a high degree of geometric precision and attaining suitable material properties in the final part. In accordance with the present invention on the other hand, 3-D manufacturing by controlled laycrvvise deposition/extraction is a novel rapid prototyping method that integrates the precision control of established subtractive processes with additive processes optimized lo produce desired material properties in order to produce a superior rapid prototyping system that does not suffer from any of the above mentioned shortcomings of prior art systems. In the controlled laycrwise deposition/extraction method of the invention, each layer is formed by selectively depositing part and complementary materials on the preceding layer (work surface). Complementary material surrounds the part material on each layer lo provide such things as structural support, chemical and/or thermal integrity, and adhesion; such being chosen based on the specific materials and ihc specific implementation of the method. Systems for selective deposition of materials are generally based on the properties of the materials and will be discussed in more detail hereinafter. Part materials are extracted from the initial part contours produced by the deposition systems lo arrive within specified geometric toleiance of (he pail mateiial layci. Selective deposition and cxli action ol complcmenlaiy malciials can be used to lot in contiol conlouis loi the selective deposition of pait malciials. These contiol contoui s ate used to guide the deposition system into pioducing neai net shape pail contoui s such lhal the amount ol subliaclivc piocessing loi the pail mateiial layci is icduccil. Piccul masks can be u.sed as a loim ol contiol contoui for selective deposition, lϊy pieloiming masks horn complcmenlaiy malciials and leaving them in place, the additive piocessing ol complcmenlaiy malciials can also be icduccd. ' The type of contiol contour and the level ol piccision in any contiol contoui will be dclei mined by the pail and complcmenlaiy malciials, Iheii lespective aiea latios ovci the woik suilace, and/oi the paiticulai cmbodimenl ol the method. In any case, each completed layer is an aggiegalc of pail matciials conlouis and complcincntaiy malciials conlouis, the pail malciials conlouis being within piespccilicd geomcliic and mateiial piopcily tolciances and the icmaining aica of the aggregate layei (woik suiface) filled with complcmenlaiy malciials. My employing vaiious deposition and cxtiaclion piocesscs, anil by maintaining stiict conliol of the piocessing enviioiimcnt, the method loi lapid piototyping ol the invention may be used with many dillcicnt malciials including, loi example, metals, alloys, thciniofoiming plastics, thcnnosctling plastics, cciamics, and salts. These dillcicnl malciials may be used simultaneously within the pait. OBJEC T OF THE INVEN TION An object of the present invention, therefore, is lo provide a new and superior method of automated manufacturing of prototypes and/or small quantities of items that, unlike pi ior ai l techniques based upon incrementally adding material to build up (he item, with altendant requirements of a high degree of precision, uses the established and precise methods of subtractive piocesscs in conjunction with additive processes optimized lo attain specified material piopertics, to provide improved rapid prototyping thai obviates shortcomings ol such prior ail techniques. A lurthcr object is lo provide novel apparatus for carrying out the novel method of the invention. Still a luither object is lo provide such a new technique of controlled layerwise deposition/extraction wherein each layer is formed by selectively depositing and removing part and complementary materials from I he current layer or work surface Other and further objects will be hereinafter described and more particularly delineated in Ihe appended claims. SUMMARY OF INVENTION In summary, from one of its broader aspects, the invention embraces a method of automated layerwise fabrication of a three-dimensional part from a computer model, through controlled deposition and extraction of materials, that comprises, providing a three- dimensional computer model leprcsentalion of the pai l and, by software, slicing the same into a plurality of successive layers corresponding lo layers of predetermined thickncss(es) of the part; generating sequences of part and complementary support materials) conlouis corresponding lo each layer; depositing nιaterial(s) for one or more contours onto a work surface within a processing enclosure; material(s) processing said deposited contoui (s) in order lo achieve prespecified material properties for part and complementary contours," removing portions of said matcrial(s) from said contour( ) under the control oT the computer model contour(s) corresponding thereto; repeating the depositing, processing, and removing as necessary under the control of the computer model corresponding to the layer to complete an aggregate layer comprising part material contours within prespecified geometric and material properly tolerances and complcmenlaiy malcrial(s) elsewhere on the aggregate layer; completing the computer model sliced layer by further processing said aggregate layer such as machining off a sublayer to ensure thickness tolerances or roughening or chemically enhancing the surface lo ensure selective binding lo the next aggregate layer,' repeating said controlled layer creation sleps lo build the entire part surrounded by the complementary malcrial/s; and removing said complementary matci ial/s to obtain the fabricated part. Picfci rcd and best mode embodiments and designs will hereinafter be described in detail DRAWINGS ' The invention will now be described in connection with the accompanying drawings, Tigs. 1 -8. which arc schematic views of necessary steps in the procedure of a preferred embodiment of the invention; Fig.'s I A and I B are (low charts of the general operation of embodiments of the invention, effecting its method of layerwise controlled deposition/extraction, with and without precul masks respectively; Fig. I allows for the first deposition lo be part or complementary matei ial; Pig. 2 is a block diagram of a preferred computer and controls subsystem for operating the apparatus and controlling the process or method of the invention; Fig. 3A illustrates suitable mask-formalion apparatus where masks are to be used, with Fig.'s 3B and 3C showing precul masks of different precision for continuous film slock and discrete film slock, respectively; Tig. 3D illustrates contour factorization thai can be used with masks; Fig.'s 3F- G and 11— J are modifications of respective Fig.'s 3A-C; Fig. 4 is a diagram of a suitable processing enclosure, work surface, and environmental contiol system; Fig.'s 5A and 513 show part and complementary materials deposition and fusion bonding apparatus used in depositing, materials processing, and adhering the successive layers in the materials additive subsystem of the invention; Fig.'s 5C and 5D respectively diagram radial and grid type discretization of the layers for the deposition of material; Fig.'s 5E, 5F, and 5G are diagrams of the primary deposition step using material spray, powder dispensing, molten material dispensing, pie-cured resin dispensing, and sol gel dispensing; \ 2 Fig. 511 is a diagram of a fusion bonding apparatus for adhering the successive deposited layers and establishing desired material properties in the layer; Fig.'s 6A and 6B are views of lascr/F-bcam and milling/grinding materials subtraction, extraction, or removal in accordance wilh the invention; Fig. 7 is a diagram of a suitable intcrlayer processing apparatus; Fig.'s 7A, 7B and 7C show a part, the layered (sliced) part, and an aggregate layer corresponding to a particular part layer. Fig.'s 8A, 8B, and 8C illustrate pai l post-processing steps of heal and surface treatment, chemical bath treatment and polishing, respectively. DESCRIP TION OF PREFERRED EMBODIMEN T(S) OF INVEN TION Before proceeding to describe embodiments illustrating the method and preferred apparatus for carrying out the layerwise controlled deposition/extraction technique underlying the invention, a brief description of the general framework lor such rapid prototyping is believed to be useful. The main subsystems associated with such rapid prototyping by layerwise controlled deposition/extraction include ( I ) a computer and controls subsystem, (2) an optional mask- forming subsystem, (3) a part chamber and work surface subsystem, (4) an environmental contiol subsystem, (5) a malci ials additive processes subsystem, (6) a materials subtractive processes subsystem, (7), a layer piocessing and prepping subsystem, and (8) a part post ¬ processing subsystem. 'This categorization is made accoiding to purpose and not according to physical realization or placement, as some subsystems may be distributed throughout the apparatus. The flow charts of Fig.'s 1 Λ and I B show the underlying 3-D controlled deposition/extraction (or removal or subtraction) processes of the invention and its various hereinafter described embodiments, employing pi cent masks and without precul masks, respectively. Rcfeπ ing first to Fig. I A, following mask formation in real lime or in batch mode and "Mask Handling", so-labeled, the part material is applied by additive processing (primary deposition and then fusion bonding), such steps also being effected wilh (he complementary material(s) (primary deposition and possibly fusion bonding), and with the deposited and bonded part material subjected lo the subtractive processing of the invention, all as more fully described hereinafter. Following rcdcposilion of complementary material 1 'ι in empty regions and subsequent surface treatment, these steps are repealed for successive layers as indicated by the feedback lines from "Surface Ti ealment" to the "Mask Formation" and "Mask Handling" process step blocks. When no precul masks arc employed on the layered prototype or part build-up. Pig. I B, the part material(s) and the complementary matcrial(s) are again applied by primary deposition and then fusion bonding (routes A and B corresponding lo part malcrial(s) fi st and complementary malerial(s) first, respectively) followed by subtractive processing of the work surface, with repetition as at ( 1 ), until the aggregate layer corresponding to a completed layer of the part is formed. Following "Surface Treatment", the process is repealed for successive layers. ( I ) Computer and Controls Subsystem The computer and controls subsystem 1 , Fig. 2, interfaces with all other subsystems and the operator lo initiate and control ihc rapid prototyping process. This subsystem lakes in a CAD/CAM representation of the prototype part and slices it, by software as indicated at ( 10), into Ihc sequence of layers (L) used to drive the remaining subsystems. This subsystem generates the process control signals ( 12) which drive the other subsystems of the apparatus, and monitors the whole process to ensure proper operation. ' This subsystem 1 ~ will generate part layers and controls based on operator preference and on minimizing process difficulties within the processing enclosure ( 14) such as part support problems, desired material properties issues, material matching problems, feature size constraints, material Mow and shrinkage problems, and woi kspace constraints, all of which ai c diagnosed \ψ front lo allow for redesign of the pail or reconfiguration of (he apparalus. 'This system also piovides mechanisms for in process diagnoses, correction, and learning. (2) Optional Mask Forming Subsystem The optional mask forming subsystem 2, Fig.'s 3A-3.I, can provide preformed mask contours lo reduce Ihc amount of materials additive and/or subliactivc processing icquired to attain the desired geometry for the pail layer. If utilized (Fig. I ), the mask formation subsystem produces masks for the deposition or the part malci ials. The mask functions as a control contour, not necessarily within tolerance, for the part materials lo fill, thereby reducing the amount of additive processing required during the formation of the layci . This is described further in the hereafter presented materials additive and subliactivc process subsystems 5 and 6, Fig.'s 5A-5H and 6Λ-6B. Furthermore, the mask contours, if made of complementary materials and left in place as support for the part contours, can significantly reduce the amount of complementary material that must be deposited to complete the layer. I lowever, (he masks may be made of materials other than complementary materials to suit the materials additive process. Nevertheless, the mask conlouis need lo be formed and positioned accurately over the work surface 'The use and precision (ranging from near net shape lo gross contours) of preformed masks in the formation of layers is a process choice to be made. ' The mask formation subsystem stores and delivers mask materials, and forms the mask conlouis maintaining mask handling and positioning control, and mask contour geometry. Additionally, this subsystem performs mask enhancements and preparations which facilitate the use of masks in (he other subsystems of the apparatus, including, positioning markers, coaling and surface treatment, material flow pathways, and bridges and/or fixtures for islands. (3) Pai l Processing Enclosure and Work Surface Subsystem ' The part processing enclosure and work surface subsystem 3, Fig. 4, contains and manipulates the part as it is being built in the enclosure ( 14), one layer at a lime ' This subsystem provides access to the part and to the current work surface (layer) of the part lo subsystems which monitor and/or operate on the part: including, for example, additive processes, subtract ive processes, positioning and/or handling systems, and probing/measurement systems. (4) Environmental Control Subsystem 'The environmental control subsystem 4, also in Fig. 4, maintains the proper environment for the subsystems of Ihc apparatus as commanded by Ihc computer and controls subsystem. 'The environmental variables which may be controlled include, temperature, pressure, inertness and other chemical conditions, cleanliness (debris and condensation), and vibration and noise (5) Malci ials Additive Subsystem ' The materials additive subsystem 5, Fig.'s 5A-5B, is comprised of the various additive processes for pai l and complementary materials. 'These processes deliver and deposit part materials within the geometric control provided by Ihe respective apparatus and/or by control contours provided by selectively deposited and extracted complementary materials or by precul masks. In addition, these systems deposit complementary materials where necessary to complete the current layer. 'The part materials additive processes have two phases: (he primary deposition phase and (he fusion bonding phase so-labeled in Fig. 5Λ. In the primary deposition phase, the material is deposited to a prespecified thickness on the work surface or only on selected discrete areas of Ihe discrctizcd (sectioned) woik surface, such as shown in Fig.'s 5C and 5D, respectively for radial and grid type di.scielizalion (sectioning). In (he fusion bonding phase, Fig. 511, il is ensured thai a fusion bond occurs between the current and previous part layers and that the deposiled material is energy treated to achieve a prespecified, set of material properties (microslruclurc). Depending on Ihc materials, the two phases may coincide and/or be achieved by the same apparatus. 'The complementary materials additive processes may have two similar phases, but it is not required that a fusion bond be established: only thai the complementary materials fill in empty areas and provide, as needed, stiuctural support, chemical and/or thermal integrity, and a substrate for future layer adhesion. Various additive processes are used within the materials additive subsystem and scheduled according lo Ihe process requirements by the computer and controls subsystem, ( 12) Fig. 2, lo achieve prespecified final part qualities. Examples of materials addilive processes include powder deposition and melting, Fig. 5F, plasma spaying and heat/energy beam glazing, Fig. 5E, olten material dispensing, and pre-cuicd mateiial dispensing and curing with heat source/energy beam (preferably procured resin and/or sol-gel and Ihc like), Fig. >. ' The materials additive subsystem incorporates surface heating, layer glazing, and rapid solidification as required for Ihc vaiious additive pioccsscs. (6) Materials Subtractive Subsystem The purpose of the malci ials subliactivc, extractive, or removal subsystem 6, Pig.'s 6Λ and 6B, is to remove part and complementary materials from the work surface as commanded by Ihc computer and controls subsystem 1 , Fig. 2. Laser or E-beam machining is shown in Fig. 6A, and milling or grinding and the like in Fig. 6B. This subsystem provides the final gcomelric accuracy of Ihc conlouis after all the potential sources of geometric error on Ihc layer such as bending/warping due lo residual stress, shrinkage upon solidification, and distortion due lo layer processing (to achieve prespecified material properties within the layer and achieve inlcilaycr fusion bonding), have already been introduced by the other subsystems. In other words, the other subsystems have all acted on (he deposited layer uch that all the physical and material piopcilics of (he layer such as material density and microslruclurc, and residual stresses aie all within prespecified tolerances for the deposited conlouis. 'The materials subtractive subsystem then selectively removes (he final materials, as specified by the respective contours for thai layer from the computer and controls subsystem I , without altering the prespecified physical and material parameters significantly. ' The use of control contours in the additive process determines the amount of subtractive processing required to arrive within the geometric tolerance oT the desired part layer. When no control contour is used, the ent ire part layer musl be formed by (he subtractive processing of the deposited part materials. Near net shape part layer contours in the mask reduces the amount of sublractive piocessing, as would a discretized malci ials additive process. After subtractive processing of the part contours, complementary materials arc deposited by the malci ials additive subsystem into empty regions of the work surface (7) Intci layer Processing and Preparation Subsystem ' The interlaycr piocessing and preparation subsystem 7, Fig. 7, consists of work surface preparations performed between each part layer as required by the computer and controls subsystem I , Fig. 2. These operations include surface treatment such as heating ( 18), roughening, grinding, leveling, etc. ( 16), addition of surfactants, binders, chemical barriers, alloying materials, etc. (20), and addition and/or configuration of fixtures. (8) Part Post-processing Subsystem 'The part post-processing subsystem 8, Fig. 8, performs finishing operations on Ihc completed part after it is removed from the part chamber. Such operations include removal of complementary malerials through oxidation or thermal/mechanical processes, Fig. 8Λ, and/or vaporization or dissolution. Fig. 8B, polishing, Fig. 8C, machining, heal treating, chemical tiealment, coalings application, and assembly. DE TAILS OF OPERATION OF SUBSYS TEMS ( I ) THROUGH (8) Referring lo Fig.'s 2-8C, the automated rapid piototyping method of the invention based on selective deposition/removal of materials is performed with (he sequences of operation previously summarized in the flow charts of Fig.'s I A and I B. 'The computer and controls subsystem I , Fig. 2, embodies, as the controls generator and system monitor ( 12), for example, a commercially available computer with CAD/CAM slicing software, a user interface, and I/O hardware by which to communicate with other subsystems. ' The slicing software exists commercially, such as, for example, the CΛMΛND and ULTRΛCΛM products from CAMΛX Systems Inc., and can readily be modified and extended, as is well known in Ihe art, to provide expert diagnosis capabilities based on materials and process variables as well as learning capabilities. If utilized, Ihc optional mask forming subsystem 2, Pig 's 3Λ-3.I, may consist o a machining station (22), Fig.'s 3A and 3E, at which continuous films or sets of sheets arc laser cut, on a system such as the Landmark laser marking system of AB Lasers Co., or machined by milling, Fig. 311, or punching to produce a precul contour for the part layer. 'The precut masks, if made of complementary material and left in place, can also serve as complementary material contours for each layer. Graphite films or sheets are one possible choice of complementary material precul masks, and may be used for high temperature applications such as with pails involving tool steels or ceramics since graphite has a high moiling temperature. Graphite also oxidizes rapidly well below its melting point which facilitates removing the graphite complementary materials surrounding the finished pai l. Different choices of complementary material may also be made depending on the process requiicmenls. These coinplemeiilaiy malci ials may then be removed by a variety o processes including heating, oxidation, solution bathing, vibration, etc.. The mask slock may be in Ihc form of a continuous film loaded into the apparatus and advanced accordingly, Fig.'s 3Λ and 313, 3E and 1 , and/or 311 and 31, or in Ihc form of discrete sheets loaded sequentially, Fig.'s 3C and 3G, and/or 3J. If utilized, Ihc precul mask contours, Fig.'s 3Λ-3J, may be rough cuts of the desired pai l contour so as to reduce subsequent subtract ive piocessing and debris. Alternatively, the pi cent mask contours may be precision machined lo within the tolerance of (he desired part layer to minimize subsequent subtractive processing and debris. In general, the degicc of precision in the mask formation process 2 would be at best equal to (he precision of (he materials sublractive process subsystem. Among the additional precul mask processing operations is the machining of Ihc mask handling and positioning markings, Fig.'s 313, 3C, 3F, 3( J, 31 and 3.1. and the forming oT removable bridges lo any mask islands which were created intentionally in favor of employing sublractive processes in particular regions of the mask. If the precul masks arc not intended lo be left as support structure, contour factorization. Fig. 3D may be used lo prevent mask islands. ' The finished precul masks are conveyed lo a mask buffer, Fig.'s 3A. 3E, and 311, from which they aic scheduled for accurate positioning, aligning, and flattening over the work sui lace in Fig. 4. The cnviionmeulal control subsystem, 4, and the part processing enclosuie subsystem, 3, arc shown in Fig. 4 as a scaled enclosure (4), with sensors, heaters/coolers, gas flow duels and pumps, and windows, for directed energy beams and sensors. The part chamber preferably consists of a servo controlled piston in a cylinder encompassed in the lower chamber enclosure ( 14), and the current work surface, Fig. 4, is shown as the topmost surface within the cylinder. The part upper chamber processing enclosure (4), houses or provides access of Ihc work surface to Ihc environment contiol subsystem 4, Ihc malerials additive and subtractive processes subsystems 5 and 6, Fig.'s 5Λ-5H and 6A and 6B, and the interlayer processing subsystem 7, Fig. 7. In the embodiment of Pig. 4, the part chamber is mounted lo a precision x-y-z positioning table, schematically represented by the 3-axis vector diagram, and the additive and sublractive subsystem apparatus aic scheduled over the work surface ' The convention is used heiein of schematically showing the lequircd positioning tables as an axis vecloi diagram, such apparatus being well known and deemed unneccssaiy lo complicate the drawings hcicin. In a modified embodiment the pai l chamber may be mounted lo a precision x and/or y and/or z positioning table and each additive and/or sublractive piocessing apparatus may be capable of x-y and/or z-axis motion in addition Ihc motion of the woik sui lace. In still another embodiment, the part chamber may be fixed and Ihc additive and/or the subtractive apparalus are capable of piccision x-y and/or z motion. The processing enclosuie and part chamber may be kept at elevated temperatures to reduce thermal cycling, residual stresses, and facilitate the malerials additive processes and the formation of quality interlayer bonds, and may provide an inert and clean enviionment via debris and contaminant removal. The processing enclosure and the pail chamber may be capable of pressure cycling for malerials additive piocessing, interlayer processing, and/or debris removal at ( I I ), Fig. 4. Additionally, the piocessing enclosure and/or part chamber houses or provides access to material stock and mask buffers which supply ihc various processes inherent to part layer formation. The processing enclosuie and chamber are designed and operated to regulate the level of oxygen, non-inert gasses (labeled "gas" in Fig. 4) and contaminants during the building ol the part. At the start of each layer one of two processing scenarios may be carried out based upon the particular embodiment and/or Ihc volume fraction of part It) complementary materials in the current layer. Scenario One: Complcmenlai y material is selectively deposited first. Part material is subsequently deposited within the control contours provided by the complementary materials. Material processing operations before described, such as heating, chemical treating, or energy treating are then performed on the deposited part materials (and possibly complementary materials) contours by the materials additive system lo ensure that Ihc part (and possibly complcmenlaiy) materials arc within tolerance of prespecified material properties. Complementary material may be deposited by either placing a precul mask made of complementary material or selectively through the materials additive subsystem, and may be machined or selectively removed in addition. ' The precision of the precul mask contour and/or the complementary materials selective deposition apparalus is a parameter of the pai ticulai ' embodiment or apparalus. Scenario Two: Part material is first selectively deposited. Complementary material may/may not be subsequently selectively deposited. Material processing operations such as heating, chemical treating, or energy treating arc then performed on the deposited part material (and possibly complementary material) contours by the materials additive system to ensure that the pai l (and possibly complementary) materials arc within tolerance of prespecified material properties. Part material may be deposited through a prccut mask or selectively through the materials additive subsystem. ' The controlled deposition and extraction of part and complcmenlaiy materials, as staled scenarios One and ' Two, is repealed lo include all part and complementary materials predetermined for the part layer. At this point in the process, the layer is at least partially covered by deposited part materials and/or complementary materials within tolerance of their respective prespecified material properties. ' The materials subtractive subsystem then processes the part contours to arrive within the specified geometric tolerance of Ihc part. Next, the materials addilive subsystem completes the layer by depositing complementary material in any empty regions of the current layer in order lo complete the layer. Materials piocessing of this additional complementary material may/may not be performed by the malerials addilive subsystem. Interlayer processing such as layer thickness control by surface machining and surface treatment and/or roughening, Pig. 7, is performed on the completed (aggregate) layer by the interlayer pi ocessing and preparation system in preparation for the next layer. All of the above occurs within a regulated environment dictated by the environment control subsystem 4 , Tig. 4,. In a pai ticulai embodiment where (he malerials sublractive system is a laser inachining system, the part conlouis may be surfaced machined in order to attain thickness tolerances before the materials subtractive system acts on the part contours. In one version of the invention as previously described, the primary deposition system may consist of a powder dispenser, Pig. 5F which deposits powder onto (he woi k surface. A roller or squeegec-like mechanism (R), is u.sed lo regulate the powder layer height and a mask may be used, if so desired, to control Ihc contour of the powder layer. Both Ihe layer materials processing and fusion bonding systems. Fig. 511, consist of a laser, such as the Diamond SL-64 made by Coherent General, electron beam, or other regional effect hcat/cncrgy source, and arc employed within an appropriate environmental cycle (e.g. temperature and pressure) lo ensure a dense, fusion bonded layer within tolerance of specified material properties, as is well known. ' This process adds bolh part and complementary materials lo Ihe work surface In a modified version, the primary deposition process may, as before described, consist o a powder or wire fed, multi-material plasma spraying system, Fig. 5E, (either multi-head or multi-material feeds) such as the SG-200 plasma spray gun based system made by Plasmadync Co.. 'The plasma spraying parameters arc chosen to regulate the layer height, and a mask may also be used, if so desired, to control Ihe tlcposilcd contour. The bonding in the plasma sprayed layer may be partially mechanical and partially from fusion, depending on the choice of spraying parameters such as stand-off distance, amperage, and gas velocity. To achieve predominantly fusion intci/intralayer bonding requires nontrivial spraying parameters, and thus a fusion bonding phase would preferably be utilized. The fusion bonding system consists of a laser or electron beam or other regional effect hcal/cncrgy source. Fig. 511, and is employed within an appropriate environmental cycle. (e.g. lempeialure and pressure, and gas concentration) to ensure a dense, fusion bonded layer within tolerance of its specified material properties. ' The additive processing of complementary materials need not include a fusion bonding phase provided thai the plasma spraying parameters can be chosen to provide a suitable support structure Additionally, rapid solidification mechanisms such as localized cooling devices may be u.sed if required for good material properties. In still another embodiment, the primary deposition phase, Fig. 5G, may embody the previously described powder or wire fed, molten material dispenser. Multiple heads or multiple material feeds allows for multiple material deposition. The molten materials dispensing parameters are chosen to regulate the layer height and a mask may also be used, if so desired, to control the layer contour. The fusion bonding system, Fig. 511, as before, consists of a laser or electron beam or other regional effect heal/energy source and is employed within an appropriate environmental cycle (e.g. temperature, pressure, and gas concentrations) to ensure a dense, fusion bonded layer within tolerance of its specified material properties. 'The complementary materials addilive process may employ either the molten malci ials dispenser or a plasma-spray head and may not icquiic a full fusion bond lo provide a suitable suppoit structure. In another modification, the primary deposition system. Fig. 5G, consists of a liquid dispenser for the before mentioned pre- cured icsin or thcrniosclling materials or for materials in sol-gel or solution form (eg. ceramics). ' The dispensing parameters aie again chosen to icgulatc the layer height, and a mask may also be used, if so desired, to control the layer contour. 'The same fusion bonding system of Pig. 511 and/or a general heal source through the environmental contiol subsystem may be used lo cure the thcrinoset or evaporate the solvent to ensure a dense, fusion bonded layer within tolerance of its specified material properties. Any of the above mentioned additive processing apparatus may be employed for ihc complementary malci ials depending on the choice of complementary material. Upon formation of the layer with or without any masking, the precision subli activc processes of Fig.'s 6A and 613, arc employed lo attain the exact geometry of the desired part. The materials subtractive processes subsystem consists, as before staled, of precision machining systems such as: milling, drilling, routing, grinding, Fig. 613, or laser or electron beam machining. Fig. 6Λ, or electrostatic discharge machining, as examples. Each such system is capable of operating within Ihc environment required by Ihc computer and controls subsystem. To this end, liquid and/or gas coolant or high temperature tooling may be employed. ' The choice of subtractive process largely depends on the materials and environment and thus various processes may be scheduled according lo need. Debris removal, as at ( 1 1 ), Fig. 4. is required to maintain a contaminant lice environment in the part processing enclosure. Debris comes in Ihc form of chips and/or loose powder and/or vapor and/or liquid from (he various material deliveries, additive and sublraclivc processes, and possibly coolants. Gas flows ("Gas", Fig. 4) may be used lo blow material vapor, debris, and other unwanted products through gas ducts and fillers such as in Ihc model 1005/1310 Punic Exhauster and Filtered Air Cleaner by KEI. Gas flows may also be used to clear areas only on Ihc work surface, as needed. Gas flows may also be induced by high pressure nozzles or by vacuum diffuscrs which are opened within the part processing enclosure during a high pressure cycle ' The gas flows may be fixed locally to the sublraclivc processing apparatus |o blow or suck debris as il is formed. More global gas flows may also be used lo suck vapors out of (he part processing enclosure with drainage paths employed to remove un vaporized liquids. Sublractive processing the part layer lo tolerance in Fig.'s 6A and 6B, moreover, may create empty areas of the work surface which require filling with complementary matei ial. 'The materials additive subsystem, Fig. 5A, discussed above, then accomplishes this task. At Ibis point in the process, the part (aggregate) layer is formed lo tolerance in the work surface plane, but not necessarily in the vertical plane (height or thickness of Ihe layer). 'The interlayer processing subsystem. Fig. 7, machines Ihc completed layer to vci lical tolerance (height) and sui lacc-prcps (roughening, adding alloying or bonding elements, chemical treating, etc.) the layer to facilitate the construction of the next part layer. In Fig.'s 7A-7C, a part is shown in Fig. 7Λ comprising 3 part malerials, as an example, with the aggregate layer being shown in expanded view in Fig. 7C for a particular part layer of Pig. 713. ' The sequences of operations outlined above arc repealed until the entire pai l is built, as described in connection with Ihc flow charts of Fig.'s I A and I B. The finished part is surrounded by complementary material which must be removed. ' The previously mentioned graphite, for example, can be removed by rapid oxidation, while other complementary materials may be removed by thermal or mechanical shocking, chemical baths or melting as shown in Pig.'s 8Λ-8C. Complcmenlaiy material may have a melting point below thai of pail matei ial, and thus may be removed by healing. Coinplemeiilaiy material may be soluble in an appioprialc liquid or gas based solvent for removal, and indeed, may be soluble in water — such as a variety of inoi ganic salts, certain waxes, or water soluble aluminum alloys. 'The complementary matcrial(s) may include glass materials such as a borosilicalc, soluble, for example, in solvents such as acetone, or may include ceramic materials of the like. As before slated, if graphite or a graphite-based material is used, such oxidizes readily under appropriate heating and/or oxygen conccnli ations. 'Thermal and/or mechanical cycling and/or shocking, as previously mentioned, may also be used for lcmoving Ihc complementary malerial(s). The invention is applicable lo a wide variety of part materials including, as examples, metals and metallic alloys, thcrinoforming and thcrmoselting plastics, waxes, ceramics, glasses, graphites, and inorganics or vai ious types, all such being deposilable in multi- material, composite layers, as described. Fuither modifications will occur to those skilled in this ai l, and such as are considered to fall within the sphere and scope of the invention as defined in the appended claims.

Claims: WHAT IS CLAIMED IS: I . A method of automated layerwise fabrication of a three-dimensional part fioni a computer model, through controlled deposition and extraction of materials, (hat comprises, producing a three-dimensional computer model representation or the part and, by soft are, slicing the same into a plurality of successive layers corresponding to layers of predetermined Ihickness(es) of the part; generating sequences of part and complementary support material(s) contours corresponding to each layer; depositing matcι al(s) for one or more of said contours onto a work surface within a processing enclosure; matcrial(s) processing said deposited contour(s) in order lo achieve prespecified material properties for pai l and complementary contours; removing portions of said ιnaterial(s) from said contour(s) under ihe control of the computer model contour(s) corresponding thereto; repeating the depositing, processing, and removing as necessary under the control of the computer model corresponding to the layer lo complete an aggregate layer comprising pail material contours within prespecified geometric and material property tolerances and complementary material(s) elsewhere on ihe aggregate layer; completing the computer model layer by further processing said aggregate layer to ensure thickness tolerances and selective binding to the next aggregate layer; repeating aid controlled layer creation steps to build the entire part surrounded by the complementary matcrial/s; and removing said complementary malerial/s to obtain Ihe fabricated part. 3/, 2. 'The method of claim I wherein (he processing of aid three-dimensional computer model into contours is done in a batch mode to obtain a full set of conlouis. 3. 'The method of claim I wherein the processing of said three- dimensional computer model for a given contour is performed as said given contour is needed by the process, with the slicing of the model occurring simultaneously with the part building. 4. ' The method of claim I wherein diagnostics and/or expert decision making arc used lo furl her process computer model data and define the slice contours to facilitate the part-building process. 5. A method as claimed in claim I and in which the materials deposition is effected upon a pre-cut mask of complementary material, Ihe cut of which corresponds lo a corresponding software-slice contour, such that Ihe mask is lefl in place as complementary support material towaid the formation of Ihe aggregate layer. 6. A method of claim 1 and in which the materials deposition is effected upon a pre-cut mask of material other than complementary material, and is removed prior lo Ihc formation of Ihe aggregate layer. 7. Ihc method ol claim 5 in which a contoui lacloii/ation appioach is used such that Ihcie aie no island conlouis lot any given mask. 8. Ihc method ol claim I in which Ihc piccul masks aie machined liamcs on a continuous film Ilia! advances ovei (he woik suilace, oi machined individual sheds that aie sequentially positioned ovei the woik suilace. 9. ' I he method ol claim I in which the mask loiniing system consists ol a conventional machining oi a lasci/cneigy beam inachining system. 10. ' Ihe method of claim I wheiein (he pail and/oi complcmenlaiy sections which loi in the aggicgalc layer may consist ol multiple malciials.

Inventors: DE ANGELIS ALFREDO, DE ANGELIS, ALFREDO
Applicants: ANGELIS ALFREDO DE, DE ANGELIS, ALFREDO
Application year: 1994
Main classification: B29C67
IPC codes: B29C67